Weyl semimetals (WSMs) is an emerging class of materials possessing unique electromagnetic properties that are not commonly achievable with conventional metals and semiconductors. The exotic phenomena emerging from the so-called Weyl nodes in WSMs where valence and conduction bands cross in single points and electrons effectively behave as Weyl fermions make WSMs very interesting for novel photonic applications in areas of non-linear optics, photovoltaics, THz electrooptics, and detection. In this work, we explore the enhancement of WSM nonlinear response by merging WSMs with the concept of plasmonics, i.e. nano-optics utilizing deeply subwavelength collective oscillations of free electrons in metallic nanostructures, and metasurfaces where arrays of plasmonic nanoantennas are used to control the phase, amplitude and polarization of the incident light. Since electrons possess non-trivial electronic states in WSMs, plasmonics could enable the observation of unique optoelectrical phenomena in WSMs with the added benefit of creating nonlinear optical elements that are smaller than the diffraction limit. Here, we realized a nanopatch plasmonic antenna array on the WSM TaAs crystal to demonstrate the enhanced non-linear optical response from TaAs. By developing a large-scale, non-destructive method of fabricating the antenna array, we address the challenge of WSM integration with photonic devices. We demonstrate a six-fold increase of the second-harmonic generation (SHG) from the Weyl semimetal TaAs surface by distributing plasmonic silver nanoantennas on TaAs.

Investigating the Moiré and Seebeck-Peltier effects in thin-film black phosphorous under excitation from a near-field plasmonic resonator we demonstrate the ability to directionally steer electrical current and adeptly manipulate temperature on the nanoscale.

Through the combination of nanoscale Mie-resonance and photothermal/thermo-optical effect, the nonlinear index n2 of both plasmonic and metal nanostructure can be enhanced by more than three orders of magnitude. We discovered various types of nonlinearity that include saturation, suppression, and reverse saturation in nanostructures. Through a similar mechanism, we also achieved optical bistability in a nanoscale resonator with a record-low Q-factor (<10) and observed large nonlinearity with hysteretic behavior. These tunable optical nonlinearities with low requirements on sample size and shape open new possibilities for the design of photonic devices and metal/semiconductor super-resolution.

This talk will introduce the latest studies on the biomedical use of metasurface. The following are the topics that will be covered: laser micro profiling; optical sectioning microscopy; light sheet microscopy; and optical tweezers.

In this research, nonlinearly two-photon pumped vortex lasing was firstly observed from perovskite metasurface. The lasing occurred at room temperature is based on the quasi-bound states in the continuum (QBIC) mode with a lasing threshold of 4.5mJ/cm2. The corresponding quality factor is around 1100. The vortex lasing mode is theoretically estimated to be a magnetic dipole mode with a topological charge of +1. In addition, the finite array size effect is found to be able to modulate the lasing. Results shown in this study should provide new ways to engineer more complex vortex beam lasing.

Discovery of novel active materials is fundamental for photonic applications. The epsilon-near-zero (ENZ) materials have been shown to be as one of the most promising optical materials in the recent years as the electromagnetic field inside media with near-zero permittivity has been shown to exhibit unique optical properties, including strong electromagnetic wave confinement, enhanced quantum emission near ENZ media, non-reciprocal magneto-optical effects, unique topological properties, and abnormally large optical nonlinearity. While ENZ optics have been investigated extensively in the last few years, the current commonly used ENZ materials suffer from limited optical enhancement because of the lack of precise control of ENZ frequency, loss, and thickness for efficient ENZ mode excitation. In addition, the active tunability and enhanced nonlinearity and emission properties in ENZ materials have yet been fully experimentally explored. This talk will review our recent studies on the active linear, nonlinear, and emission properties of conducting oxide and metallic nitride epsilon-near-zero materials in planar and optical fiber platforms [1-7]. I will present a method to engineer the field intensity enhancement of the Al-doped zinc oxide (AZO) ENZ thin films synthesized by atomic layer deposition (ALD) technique. I will then discuss the observation of abnormal nonlinear temporal dynamic of hot electrons and enhanced optical nonlinearity in AZO and ITO ENZ thin films under different pump fluences and excitation angles using a degenerate pump-probe spectroscopy technique. I will present the first comprehensive study of photoluminescence from a 2D material placed near ENZ films and its dependence on the losses of materials, as well as the spectral response of such emitters with excitation wavelengths across the ENZ regime. Finally, I will also discuss the first experimental demonstration of optically confined ENZ resonance excitation in an optical fiber waveguide uniformly coated with AZO nanolayer. These studies enrich the fundamental understanding of emission and nonlinear properties on ENZ thin films and the integration of ENZ materials and optical fiber will open the path to revolutionary ultracompact in-fiber optical devices for optical communication, imaging, sensing/laser applications.

The design of multilayer ENZ stacks is challenging due to the many parameters involved, including the number of layers, thicknesses, ENZ wavelength, and optical losses. Our machine learning-based approach enables us to efficiently search through the vast design space and experimentally verify the performance of the resulting thin film stack. The resulting 2-layered AZO ENZ thin film stack achieved perfect absorption of light (> 95%) in the near-infrared region from 1500 nm to 2500 nm, highlighting the potential of machine learning techniques in designing ENZ materials for a range of applications.

Fluorine-doped indium oxide (IO) nanocubes separated by nanometric gaps constitute a versatile system hosting high-quality mid-infrared plasmons with potential application in optoelectronics and light harvesting. In this theory-experiment combined work, we predict large tunability of these hybridized plasmon modes by controlling the gap size and the dimensionality of the gap region. We confirm this prediction through electron energy-loss spectroscopy (EELS) measurements performed in a scanning transmission electron microscope (STEM). Our theorical-experimental results elucidate the influence of gap geometry on the coupled plasmons and field concentration in doped IO nanostructures, and further suggest exciting applications in plasmonic sensing and surface-enhanced spectroscopies.

Plasmonic color printing with semicontinuous metal films is a lithography-free, environment-friendly method for getting bright, non-fading colors. Such films comprise islands – metal nanoparticles and their clusters of various dimensions, which resonate at different wavelengths upon external light illumination depending on the size and shape of the local particle structures. When impinged, a focused laser beam can locally modify the film morphology through thermally induced changes resulting in various optical spectra and colors. It is an inexpensive, simple method of generating a wide range of bright contrasting colors and is also feasible for large-area macroscopic coloration.

We successfully tuned optical properties over a wide wavelength range and obtained full colours using random nanostructures based on Nanophotonics and Plasmonics. The colors realized full coverage standard RGB color space, and the structure achieved as high color quality as the periodic structure. We also found that the optical properties of Au and Ag nano-disk structures fabricated by an electron beam lithography can be improved by very simple heat treatments. We also introduce a novel method to improve the emission efficiencies of InGaN/GaN quantum wells by depositing dielectric thin films instead of metals and UV laser irradiation.

We propose a thermal management technique using metamaterials, which enables the gathering and release of thermal energy from the surrounding environment. A metamaterial is an artificial material that works as an antenna that absorbs thermal radiation emitted from the surrounding medium and a transducer that converts the absorbed energy into local heating. Thanks to its high absorption coefficient, metamaterials can efficiently gather electromagnetic waves. By utilizing this technology, we have demonstrated metamaterial thermoelectric conversion, which can generate electricity even in an environment with a uniform temperature distribution. Additionally, we propose a non-radiative cooling technique, which operates as the reverse process of metamaterial thermoelectric conversion.

We experimentally demonstrate the dominating nonlinear saturable absorption contributed by conduction band electrons in epsilon-near-zero (ENZ) transparent conducting oxide (TCO) thin film when the plasmon-polariton mode near the ENZ regime is excited (ENZ mode). Using our engineered TCO indium tin oxide (ITO) thin film that allows three-photon absorption near the ENZ regime, we study the nonlinear absorption dynamics with z-scan nonlinearity measurement technique. We observed the competing behavior between the electrons in the valance and conduction bands at a fixed pulse intensity and various angles of incident. Our results are significant for advancing efficient all-optically tunable devices.

Waves propagate diffusively through disordered media due to random scattering. Though most waves are reflected, only a small fraction carries information from deep inside the medium. These remitted waves are widely used for noninvasive probing from seismic interferometry to diffuse optical tomography and functional near-infrared spectroscopy. The meager signal-to-noise ratio of remitted waves eventually limits the probing depth. By tailoring spatial wavefront of a laser beam, we enhance remitted signal by an order of magnitude, and increase its sensitivity to local changes inside an opaque medium. This work illustrates the potential of coherent wavefront control for noninvasive diffuse-wave imaging applications.

Valley photonic crystal (VPhC) is one of the photonic nanostructures that can host topologically protected edge states. The edge states enable efficient light guiding even under sharp corners. At a bearded interface consisting of two topologically distinct VPhCs, the edge state can be an in-gap slow light mode while keeping its robustness against sharp corners. The loss at sharp waveguide bends is largely suppressed for the topological slow light mode, compared to the non-topological slow light mode. Here, we discuss the design and the experimental demonstration of topological slow light waveguides in semiconductor VPhCs.

We represent AI-designed metasurfaces and three low-cost manufacturing: 1) nanoimprinting with high-refractive-index dielectric particle embedding resin (PER), 2) bandgap engineering of hydrogenated amorphous silicon (a-Si:H), and 3) atomic-layer coating on imprinted resin. a-Si, TiO2, and ZrO2 PERs are used for metasurfaces at infrared (940 nm), visible (532 nm), and ultraviolet (325 and 248 nm), respectively; measured efficiencies reach 47% (940 nm), 91% (532 nm), 72% (325 nm), and 49% (248 nm). PER metasurfaces with an inverse design provide 3D, full-color holography at visible. The bandgap of a-Si:H is engineered to suppress optical losses, realizing metasurface efficiencies of 42% (450 nm), 65% (532 nm), and 75% (635 nm)[6]. We deposit an atomic layer on resin for 12-inch metasurfaces, achieving measured efficiencies of 61% (450 nm), 78% (532 nm), and 65% (635 nm).

We discuss our recent results in nanophotonic properties of engineered naturally hyperbolic van der Waals materials. We thermomechanically control thin MoO3 flakes to tune their crystallographic and phonon-polaritonic properties. We show induction of an irreversible strain of up to -2.4% and tuning of the phonon-polaritonic dispersion relationship by more than 10%. By patterning a nanohole array in the exfoliated flakes, resonant phonon-polaritonic excitations result in more than an order of magnitude in mid-infrared field enhancement, resulting in a strong experimentally verified near-field response and enhancement of nonlinear optical properties.

Experiments demonstrating extremely rapid modulation of the permittivity have been performed by exploiting the enhanced non-linear effects possible in the presence of plasmonic resonances [1]. These experiments measure an extreme rise time by exploiting the analogy between Young's slits and closely spaced time windows which produce diffraction in frequency space. I go on to discuss some theoretical consequences of space-time modulated structures which can be understood as a series of optical event horizons where wave energy can be trapped and amplified, leading to radiation from the quantum vacuum state. [1] Romain Tirole et al (2023) arXiv:2206.04362

We present the use of Moiré metalens in fluorescence microscopy system combining with telecentric system and HiLo algorithm for bio-imaging. The Moiré metalens is composed of paired phase metasurfaces. The system is capable of tuning the focal length from 10 mm to 125 mm by tuning the relative angle between the paired metasurfaces without axial displacement. In addition, the speckle illumination HiLo microscopy is used to mitigate the out-of-focus light scattering, the background noise. The labeled beads and ex vivo mouse intestinal tissue samples are imaged to show the optical sectioning capacity of our system. It is anticipated that the proposed design of varifocal metalens would have significant applications in fluorescence microscopy and endoscopy.

This talk focuses on a new paradigm for dynamic reconfiguring arbitrary output wavefronts using control systems with the same degrees of freedom. A fast beam steering technology based on reconfigurable metasurfaces driven by an in-plane two-degree-of-freedom (2DOF) mechanical actuation system will be demonstrated, which measured a 6-kHz modulation speed and a "±65.6° " field of view. Finally, its applications in lidar and scan imaging will be discussed with the primary results.

We have studied dispersion of surface plasmon polaritons (SPPs) in the Kretcshmann’s geometry (prism/Ag/dye-doped polymer) in weak, intermediate, and ultra-strong exciton-plasmon coupling regimes. The dispersion curves obtained in the reflection experiment, were in a good agreement with the simple model predictions at small concentrations of dye (Rh590 and Rh610) in the polymer (PMMA). At the same time, a highly unusual multi-segment ladder-like dispersion curves were observed at extra-large dye concentrations. The dispersion curves observed in polymers co-doped with two dyes (Rh590 and Rh610) suggest strong coupling of excitons in the Kretchmann’s geometry. Acknowledgments: NSF 1856515, DOE/NNSA DE-NA0004007.

Ultra-thin, monocrystalline gold microflakes open new opportunities for the study of light absorption and light emission processes. We report results on synthesis and nanostructuring, photoelectrochemical conversion and photoluminescence emission in this unique system.

In this work, we conducted nanoscale imaging of both the Raman peaks and electron Raman scattering to study the strain and doping of graphene wrinkles and compared the varying Raman spectral characteristics to flat graphene using tip-enhanced Raman spectroscopy (TERS). We found that on the wrinkle, anisotropic strain and non-uniform doping was present. We also found that the G band peaks were broader on the flat graphene as compared to on the wrinkle and attribute it to the plasmon-mediated excitation that opens other possible paths for electron-hole recombination due to the high electric field confinement underneath the tip apex. A broad background continuum that we surmise is electronic Raman scattering originating from both the graphene monolayer and the Au(111) substrate was observed and when imaged has a strong correlation to the TERS images of the Raman peaks.

I will show how to employ temperature-dependent plasmon-exciton coupling spectroscopy to determine the relative energies between spin-allowed bright excitons and spin-forbidden dark excitons in monolayer transition metal dichalcogenides and how to utilize different plasmonic nanocavities to achieve selective emission enhancements of bright and dark excitons.

In the present talk, we discuss strategies to design both plasmonic and all-dielectric active metasurfaces, which can dynamically manipulate the wavefront of the transmitted light in the near-infrared wavelength range. Our active transmissive metasurfaces feature an array of amorphous silicon (a-Si) pillars on a silica (SiO2) substate, which, in some cases, are hybridized with a thin metallic layer. The optical response of the designed metasurface is either tuned thermo-optically or by integrating active materials such as lithium niobate (LNO), indium tin oxide (ITO), or tungsten disulfide (WS2) into the metasurface structure.

We present our recent progress in developing material platforms for dielectric and metallic metasurfaces. We also discuss some novel methods for fabrication of metasurfaces and demonstrate selected applications.

Plasmonic metasurfaces, i.e., ultrathin arrays of engineered metallic meta-atoms, have attracted increasing attention due to their unprecedented capabilities of molding classical light. Despite significant progress, most existing metadevices to date are passive and lack real-time dynamic modulation post-fabrication. Therefore, it is highly desirable to realize tunable metasurfaces with functionalities actively controlled by applying external stimuli, which are promising for more intelligent and adaptive systems. In this talk, I will talk about a piezoelectric MEMS-empowered dynamic metasurface platform for active wavefront shaping by electrically varying the gap between the MEMS mirror and the designed optical metasurface layer. In particular, I will introduce how to achieve full-range birefringence control and tunable chirality.

In the first part, by integrating a solid nano-structure with its inverse complementary, I will report a plasmonic metasurface with a circular cross-polarization conversion efficiency higher than 50% in transmission at near-infrared wavelengths. Such high optical performance metasurface is achieved by simultaneously exciting the multipolar modes, which satisfies the toroidal-assisted generalized Kerker condition. We switched from free space components to integrated devices for the second topic. We propose that the polarization state of a lasing emission can be actively modulated at the source with a metasurface-engaged microcavity, including highly circularly polarized, linearly polarized, or elliptically polarized lasing emission.

All-optical switches enable ON/OFF conversion function by following the concept of light-controlled-by-light and are highly significant due to their potential to overcome speed limitations set by electrical switches. In this talk, the ultra-fast responses of metamaterials at the effective epsilon-near-zero (ENZ) wavelengths and/or resonant wavelengths, unveiling response times down to a few hundred femtoseconds (fs), will be presented. Especially a novel Si-compatible hyperbolic metamaterial based on Titanium nitrides (TiN) and indium-tin-oxide (ITO) multilayers that possess two different ENZ wavelengths will be presented with the switching time, measured in pump and probe, of the metamaterial at both ENZ ranges.

By combining optical and x-ray transient data, we access the excited electron system and lattice of gold nanoparticle. The particle expansion starts already with the optical excitation pulse and thus occurs in the kinetic limit of the electron gas excitation. We present a new microscopic, parameter-free model that reproduces the experimental observations and leads to insight into ultrafast phenomena, which are addressed by the sampling of transient optical fields.

Plasmonic devices exhibiting asymmetric responses depending on the propagation direction of the incident wave have attracted great attention due to the variety of optical applications. Such structures allow adapted electromagnetic responses with large additional degrees of freedom. Here, we proposed and numerically demonstrated that asymmetric electromagnetic response can be realized in a plasmonic structure. The proposed plasmonic device is composed of a periodical grating of metallic rotated elements embedded in a continuous dielectric medium, we consider incident waves propagating in opposed directions and we show asymmetric behavior for the absorption and reflection and they can be controlled by adjusting the optical and geometric parameters of the metallic element as well as their rotation. Asymmetric values of absorption and reflection with values higher than 80% of asymmetry can be obtained. The structure shown here can be used as absorber or mirrors for visible and infrared radiation.

Meta-lens is an innovative planar optical device that uses subwavelength nano-antennas to control the wavefronts of light, enabling modulation for various applications. This study proposes a series of intelligent imaging systems based on meta-lenses for aerial, underwater, and land applications. Specifically, monocular, binocular, and multilocular meta-lenses are designed and fabricated for aerial, underwater, and land imaging and sensing applications, respectively. With the support of artificial intelligence, real-time intelligent sensing perception is achieved. This study expands the application scenarios and practical value of meta-devices, enabling mini-robots, autonomous systems, and advanced sensing for operating in multiple scenarios.

We experimentally demonstrated an unprecedented simple way to excite strong and broadband toroidal dipole (TD) response in the optical regime using dielectric metasurfaces upon plane-wave excitation. A comprehensive study of the geometric dependence for the TD mode was performed. In addition, with the change of local refractive index surrounding dielectric nanopillars, the TD mode was found to reach a sensitivity of 459 nm per external refractive index (RIU) change, showing good correspondence to our numerical prediction of 470 nm/RIU. In addition, arrays of tilted angle of nanorod pairs were designed to sustain quasi-bound states in the continuum (quasi-BIC) with TD and electric quadrupole (EQ) resonant property, showing strongly optical fields at the surface of tilted nanobar pairs and resulting in a measured (simulated) sensitivity and figure of merit of 608 nm/RIU and 46 (612 nm/RIU and 85), respectively.

Tamm plasmon polaritons (TPPs) resonance is excited within a DBR stopband with a metal film. Here, TPP sensors is proposed with Pd on top to detect the low hydrogen concentrations. In addition, TPP photodetectors with a graphene layer show high responsivity and selectivity for wavelength and angle, making them suitable for LiDAR detection and navigation instruments.

We have successfully designed, fabricated, and demonstrated the use of a planar dielectric metasurface to generate AAF beams for biomedical applications. Our results demonstrate the potential of using metasurface for precise control of the local phase of light and the generation of unique optical properties. The high-intensity contrast between the initial and focal plane was used for fluorescence-guided light treatment of microspheres and mouse cardiac slices. Our ultrathin (800 nm) Nano-photonics metasurface allows for designing miniature integrated optical devices for biomedical instruments. The AAF beam& #39;s high-energy-density hotspot could be useful in Nano-surgery, high-resolution imaging, and photo-dynamic therapy.

The divergent physical properties of light and sound waves result in tradeoffs between resolution and penetration depth with respect to their imaging capabilities. An ideal imaging system should combine the strengths of optical and acoustic imaging. Here, we demonstrate that via the use of designed metal nanoparticle based plasmonic metasurfaces, we can enable photoacoustic imaging with resolution better than optical imaging and penetration depths as deep as acoustic imaging, without any destruction of media, and with reduced power requirements (via plasmonic focusing). Moreover, the application to photoacoustic structured illumination microscopy would lead to new avenues in miniaturized, on-chip super-resolution imaging.

Incorporating plasmonic metal nanostructures with the semiconductor compounds offers a new route to significantly improving the performance of photodetectors. Herein, we developed five hybrid structures to demonstrate ultrasensitive photodetection in in MIR, visible and UV regions, respectively. These five demonstrations are, 1. Plasmonic Metasurface Integrated Black Phosphorus-Based Mid-Infrared Photodetector with High Responsivity and Speed, 2. Ultrasensitive Gateless Photodetector based on 2D Bilayer MoS2-1D Si Nanowire-0D Ag Nanoparticle Hybrid Structure, 3. Enhanced Photoresponsivity of Perovskite QDs/Graphene Hybrid Gate-free Photodetector by Morphologically Controlled Plasmonic Au Nanocrystals, 4.Ultrasensitive Photodetection of Monolayer MoS2 using Semimetal Plasmonic Structure and Ohmic Contact, and 5. A Multifunctional Plasmonic Sensor for Excellent UV Photodetection and NO2 Gas Sensing by an Array of Al Nanocaps on GaN Truncated Nanocones.

We will discuss recent progress in the synthesis and characterization of atomically thin noble metal structures, comprising a few atomic layers, and sustaining plasmons of high quality. These materials constitute a viable solution to the control of visible and near-infrared light over few-nanometer scales. We will further explore the ultimate limits of plasmon lifetime and spatial confinement, as well as applications to optical sensing and optoelectronics.

The strong light-matter interaction enhanced by surface plasmons are well known to be the enabler for various applications such as sensing, imaging, catalysis, and heat generation. In particular, surface plasmon resonance is the central working principle for the selective absorber in commercial solar heaters. On the other hand, reversing the optical properties of a selective absorber will result in sub-ambient radiative cooling. This invites the question of whether we can step further to dynamically tune the optical properties so that the heating/cooling energy utilization or even more functionalities can be realized on the same device. Fundamentally, this requires in-depth knowledge of the structure-property-synthesis relationship of plasmonic materials that can be controlled in a dynamic, reversible, and efficient manner.

Micro-Light emitting diodes (µLEDs) are attracting broad interest because of their low power consumption, compact size and high brightness. However, µLEDs suffer from low outcoupling efficiency due to the high refractive index mismatch between air and the semiconductor. Recent progress in nanophotonics has led to the demonstration that metasurfaces integrated with emitters can provide an opportunity for tailoring the emission. We have designed and fabricated plasmonic metasurfaces onto a GaN/sapphire wafers to tailor the emission of InGaN quantum wells for µLEDs. We have investigated the far-field photoluminescence emission of samples with different metasurfaces, optimizing the light emission and outcoupling.

The plasmonic-photonic mode coupling and the sensing performance of Au nanoslits/distributed Bragg reflector (DBR) around the Rabi splitting (RS) generated by surface plasmon polariton (SPP) and Tamm plasmon states (TPs) were investigated. In the RS region, some original TPs electromagnetic fields were extracted, reducing original SPP fields while generating TPs-like fields in the DBR. Through the spectral integration method, the bulk sensitivity at the region of RS and outside of RS (period of 600 nm) are 403 and 203 nm/RIU, respectively. That is, hybrid SPP-TPs mode provides enhanced evanescent field than single SPP mode.

For applications from optical sensing to photoemission spectroscopy, it is desirable to pattern a plasmonic surface and enhance, over a large area, the field intensity near the surface. What is the largest possible large-area field enhancement? Here, we show a simple semi-analytical bound, based primarily on power-conservation principles, that dictates the fundamental limits to large-area plasmonic field enhancements. Our bounds depend only on the material permittivity and the angle of incidence. Our theory predicts that > 1000X field enhancements are possible with patterned silver metasurfaces. Through numerical optimization, we discover structures that achieve enhancements over 97% of the fundamental limit, for designable wavelengths across the visible and near-infrared.

In this work, we report a novel method to mitigate the dependency of incident angle on diffraction efficiency by depositing a metal film on the grating structure. Moreover, the metallic structures strongly enhance the interaction between the incoming light and the nanostructures, leading to an improvement in diffraction efficiency. The results have shown the potential to overcome the bottleneck of augmented reality glasses, which require a large field of view with high efficiency.

Gold nanourchins (GNUs) have a multitude of tips-and-dips which make them excellent SERS substrates. Herein, GNUs were obtained via a two-step synthesis integrated in a controllable microfluidic setup. GNUs were bio-functionalized with a reporter molecule and a polymeric coating. The detection system relies on antibodies that recognise the cancer biomarker CEA-CAM5. Antibody-antigen binding leads to a proportional aggregation of the particles and SERS enhancement. Integration of the detection system in a microfluidic platform offers a multitude of advantages. Acknowledgement: This work was supported by MCID, CNCS-UEFISCDI through proj.nr.PN-III-P1-1.1-TE-2021-0234 within PNCDI-III, and through the Core Programme proj.nr.PN.23.24.01.02 within PNCDI 2022-2027.

Surface enhanced Raman scattering (SERS) signal fluctuate due to position between near field and adsorbed molecules. According to past works, the frequency of the bright period follows a power law. The purpose of this study is to analyze the blinking behavior of SERS spectra by Density-Based Spatial Clustering Analysis with Noise (DBSCAN) with temporal resolution higher than a conventional spectroscopic method. As a result, it was confirmed that the SERS blinking actually follows the power law even under adverse conditions such as extremely low sample concentration and a very short exposure time of 10 ms.

Three-dimensional optical Yagi-Uda nanoantenna array are fabricated using Nanospherical-Lens Lithography (NLL). The fabrication method can produce nanoantenna array that covers large area and with high throughput. The individual Yagi-Uda nanoantenna is consisted with 3 Au nanodisks separated by a thin layer of SiO₂ obtained through sequential evaporation using NLL. The operation wavelength of the nanoantenna is designed is in the near infrared, which can be easily controlled by varying the structural parameters during NLL. We believe the results shown in this study can be applied to obtain directional antenna of nano-emitters and receivers in the near future.

The accumulation of Gouy phase is a well-known phenomenon associated with propagation of Gaussian beams passing through a focal waist in free space. The Gouy phase can be understood from a purely heuristic perspective as the effect of change in optical mode volume [1], and as such does not have to be restricted to Gaussian beams. Here I demonstrate that an evanescent field of surface waves, which undergoes adiabatic tapering along its propagation also accumulates a (transverse) Gouy phase in addition to the conventional dynamic and Gouy phase due to its propagation along the surface. The theory of this effect, built on the calculation of the average value of the distribution of wave-vector components [2], is developed for the case of the evanescent field of a surface plasmon guided by a thin conductive layer with spatially changing surface conductivity. A non-uniform electric bias of a single layer graphene, which gives rise to the spatially non-uniform Fermi level and surface conductivity, is proposed as an approach for experimental testing of this effect. The accumulation of the Gouy phase of surface plasmon guided by such nonuniformly biased graphene layer is confirmed by numerical simulations. The discovered effect promises a new approach to actively control phase in plasmonic devices and can be useful for a variety of practical applications, from interferometry to sensing.

In this paper, we present an approach to improving the performance of surface relief type augmented reality (AR) glasses by introducing the gap plasmonic mode at the input coupling grating. Our results demonstrate that the gap plasmonic mode interacts with the incoming light from the light engine, leading to a significant increase in diffraction efficiency at the desired wavelength range. Moreover, the proposed structure exhibits a high diffraction efficiency at a wide angle of incidence, thanks to the magnetic mie resonance mode at the gap plasmonic mode. We used a DOE waveguide consisting of an incoupler and an outcoupler and compared the efficiency by measuring the eyebox efficiency at a certain distance from the outcoupler. The metal used for deposition was silver, and we observed a final efficiency increase of 3-4 times.